Typographic Stippling Controls

• Auto-map weights to background density on load.
• Mouse click + drag: darken letters; Shift + drag: lighten.
• 1–9: set fixed weight; 0: reset fixed weight.
• A–F: set background opacity (0–100%).
• Shift+Z: toggle 25% preview zoom (scale).
• Shift+X: toggle background canvas visibility (shows sampling).
• Shift+Y: toggle fast/quality rendering mode.
• Shift+D: toggle diagnostics.
• S: save HTML (filename prompt).
• H: hide/show this help.

Tip: show the background canvas with Shift+X to confirm sampling alignment.